Casting Method and Casting Installation for Aluminium or Aluminium Alloys

ABSTRACT

The invention relates to a casting method for aluminium or aluminium alloys, in which molten aluminium is treated and fed to at least one casting station ( 33, 34 ), in which the molten metal is cast into semi-finished products or similar. A number of casting ladles ( 25 ) are used to treat and feed the molten aluminium to the respective casting station ( 33, 34 ). The ladles are filled with the molten metal and the latter is then transported to at least one additional stage ( 32 ), where it is treated. The molten metal is subsequently delivered in the ladles ( 25 ) to the casting station ( 33, 34 ), where the ladles ( 25 ) are emptied. The invention thus provides an efficient method that can be flexibly adapted to the time periods of the process, said periods altering according to the situation.

The invention concerns a casting method for aluminium and/or aluminiumalloys in accordance with the generic term of claim 1 and also a castingmachine for implementation of the method.

Casting methods and casting machines for aluminium and/or aluminiumalloys are known in the art, in which solid or liquid aluminium ismelted in a smelting furnace and then retained in a refining furnace,from which the molten aluminium flows via a long channel to a castingstation and is thereby exposed to different treatments. Thus, alloyadditions are added to the molten aluminium flowing down the channel andan inert purging gas (argon) is injected, before the melt, via a filter,reaches the casting station, in which it is cast into semi-finishedproducts (cf. FIG. 1 in which an ordinary casting machine for aluminiumis shown diagrammatically). Only limited homogenisation of the moltenaluminium is possible. The treatment times are tied to the castingprocess and thus predetermined and limited in terms of time.

The individual treatment stations have to be co-ordinated with eachother perfectly. If one of the stages of this in-line machine does notfunction, then the entire casting machine has to be shut down. The longchannel through which the molten aluminium flows means a loss oftemperature so that the material has to be overheated in the refiningfurnace so that a sufficient temperature can be reached on arrival atthe casting station. Extensive casting times mean that the smelting andrefining furnace has to be available for the entire casting time, beforethe next batch of melt is used. The energy consumption of the furnacesis correspondingly high. Normally, reverbatory furnaces with hydrocarbonfuel are used, giving rise to the disadvantage of a rapid absorption ofhydrogen from the burner flame. Furthermore, greenhouse gases and otherpollutants which load the atmosphere are also created. The long, openchannel through which the molten aluminium runs, however, also meansthat the metal absorbs hydrogen from the atmosphere and causes theformation of dross.

The present invention is based on the problem of proposing a moreeconomical and more flexible casting method for aluminium and/oraluminium alloys and also of creating a casting machine to implement themethod, enabling an optimal period for the treatment and casting of themolten aluminium and thereby achieving an improved quality of thesemi-finished products to be produced.

This problem is solved according to the invention by a casting methodwith the characteristics of claim 1 and by a casting machine with thecharacteristics of claim 13.

Preferred refinements of the casting method according to the inventionand of the casting machine according to the invention form the subjectmatter of the dependent claims.

By making use of ladles in accordance with the invention for thetreatment and feeding of molten aluminium in controllable sequences,preferably to several casting stations, this phase of the method isdecoupled in terms of time from the actual casting process. Theindividual treatments are no longer fixed and temporally restricted, butcan if necessary be adapted until the desired quality of the moltenaluminium to be cast is achieved in the relevant ladle.

The method according to the invention is considerably more efficientthan the in-line method since there is no longer any need for largerefining furnaces. If used at all, the furnaces are used for smeltingand heating, but not for keeping warm over longer periods. These can bein the form of energy-efficient and ecologically advantageous inductionfurnaces.

The invention is next explained in more detail with the aid of thedrawings, which show:

FIG. 1 diagram of an embodiment of a state of the art casting machinefor aluminium; and

FIG. 2 diagram of an embodiment of an aluminium casting machineaccording to the invention.

FIG. 1 shows a state of the art casting machine 1 for aluminium and/oraluminium alloys. Liquid or solid aluminium is introduced as basicmaterial in a first stage or station 2, which comprises a smeltingfurnace 3 and a refining furnace 4 attached thereto. For example, thealuminium can be supplied from a potroom by means of a transfer ladle 5or as a scrap batch. The furnaces 3, 4 are usually large reverbatoryfurnaces using hydrocarbon fuel. The melt produced in the smeltingfurnace 3 is heated in the refining furnace 4 to the necessarytemperature and partly homogenised by agitation.

Once the molten aluminium has reached the necessary temperature, it isguided out of the refining furnace 4 via a long channel 6 to a castingstation 7, whereby it flows through various treatment stations 11, 12,which together with a filter 13 connected upstream of the castingstation 7 form a second stage 10 of the casting machine 1. In thetreatment station 11, various alloy additions are added to the moltenaluminium. Gas purification occurs in the treatment station 12.

The casting station 7, in which the molten aluminium is cast intosemi-finished products, can be operated continuously orsemi-continuously in a way known in the art and therefore not describedin more detail.

The treatment periods in the second stage 10 are tied to the castingprocess to be carried out in the casting station 7 and thuspredetermined and restricted. The individual treatment stations 11, 12must be perfectly synchronised with each other in their function. If oneof the stages of this in-line machine does not function, then the entirecasting machine 1 has to be shut down. The long channel through whichthe molten aluminium flows means a loss of temperature so that thematerial has to be overheated (e.g. to 730° C.) in the refining furnace4 so that a sufficient temperature (e.g. 700° C.) can be reached onarrival at the casting station 7. Extensive casting times mean that thesmelting and refining furnace 4 has to be available for the entirecasting time, before the next batch of melt is used. The energyconsumption of the furnaces 3,4 is correspondingly high.

In reverbatory furnaces with hydrocarbon fuel, the disadvantage arisesof a rapid absorption of hydrogen from the burner flame. Furthermore,greenhouse gases and other pollutants which load the atmosphere are alsocreated. The long, open channel 6 through which the molten aluminiumruns, however, also means that the metal absorbs hydrogen from theatmosphere and causes the formation of dross.

FIG. 2 shows a diagram of a casting machine 1 according to the inventionfor aluminium and/or aluminium alloys. The first stage of the castingmethod according to the invention occurs in a filling station 21, inwhich hot molten aluminium is poured into a number of ladles 25. Theladles can for example have a capacity of 15 t. Either liquid, hot(temperature approx. 900° C.) aluminium from a potroom can be poureddirectly into the ladles 25 using transfer ladles or at least one,preferably several, furnaces 22, 23, 24 are assigned to the fillingstation 21 and are responsible for delivering the molten aluminium,whereby in addition to liquid aluminium, scrap aluminium or ingotsprovided for recasting can serve as basic material. The molten aluminiumcan for example be poured into one of the ladles 25 at half-hourlyintervals. Advantageously molten aluminium of varying quality (withdifferent degrees of aluminium purity) can be poured from the individualfurnaces into the ladles 25, whereby the filling of the ladles 25 withmolten aluminium, possibly also with mixed material from variousfurnaces 22, 23, 24, can be computer-controlled.

Preferably, electrical induction furnaces can be used as furnaces 22,23, 24, which are considerably more efficient in energy terms thanreverbatory furnaces. These can for example be induction furnaces with acapacity of 20 t, from each of which 15 t of molten aluminium can bepoured into one of the ladles 25 and the remaining 5 t can serve whensmelting a further charge.

The casting machine 1 according to the invention has a purification andpreparation station 30, from which purified and pre-heated ladles 25 aare transported to the filling station 21 for filling (ladles 25 on atransport section are generally designated in FIG. 2 by the letter T).By pre-heating the ladles 25 to, for example, 900° C., the moltenaluminium poured from the furnaces 22, 23, 24 operated at a temperatureof approx. 800° C. can remain for longer in the ladles 25 until it fallsto the typical casting temperature of 700° C., as would be the casewithout pre-heating.

After the respective ladles 25 have been filled, the dross is skimmedoff the surface of the melting bath (dedrossing) by tilting the ladle.

The ladles 25 filled in the filling station 21 are transported to atreatment station 32, in which the second stage of the casting processoccurs. Firstly alloy additions are added to the molten aluminium (cf.the ladles referred to as 25 b in FIG. 2). (However, it is also possiblefirst to place at least part of the alloy additions in the cleanedladles 25 a before pouring in the melt.) After that the molten aluminiumis homogenised and purified (cf. ladles 25 c). To this end, the ladlesare placed beneath a rotary impeller immersible in the respective ladles25 c to inject inert gas, e.g. argon or nitrogen, whereby combinedhydrogen removal, homogenisation and/or thermal regulation of the moltenaluminium can occur. The injection of argon eliminates the absorption ofhydrogen from the humidity present in the atmosphere and the formationof dross is reduced. To remove alkali trace contaminants, small amountsof chlorine can be added into the purge gas.

Following treatment of the molten aluminium the ladles 25 can be kept instorage stations provided for this purpose (in FIG. 2 such storagestations are generally designated by the letter S), until a castingstation 33 or 34 is available. The casting machine 20 preferably hasseveral such casting stations (two shown in FIG. 2), to which the ladles25 can be transported from the treatment or storage station, and inwhich the molten aluminium is cast into semi-finished products.

The temperature of the molten aluminium is maintained advantageously bycovering the ladles 25 with a cover.

During the time spent in the storage station S, the temperature in theladles 25 can be reduced by the injection of argon through a porous plugin the base of the ladle or maintained or increased by means of a smallburner built into the ladle cover.

The emptying of the ladles 25 d at the respective casting station 33, 34occurs through the base of the ladle by means of controllable opening ofa sliding closure, whereby the outflowing molten aluminium is guidedinto a collector spout, preferably encased by an inert gas. During thisphase, too, argon can be blown in through the porous plug in the ladlebase, agitating and purifying the melt. By covering the ladles 25 d,inert atmospheres can be created in their upper area, which reducesoxidation and absorption of hydrogen.

The casting stations 33, 34 are each equipped with a filter system in away known in the art and are operated continuously or semi-continuously.

After emptying the ladles 25 d, these are transported to theaforementioned cleaning and preparation station 30 where they arecleaned (cf. ladle 25 e) and prepared for re-use, in particularpre-heated (cf. ladle 25 a). The emptied ladles can also be stored untilfurther use in the storage stations S provided for this purpose.

There are multiple routes provided to transport the ladles 25 from onestation to the next or to the storage stations (S), whereby the ladles25 can be transported on rails or by means of overhead hoists.

The casting machine according to the invention is equipped with acontrol system to control the charges to be poured out of the individualfurnaces 22, 23, 24 into the individual ladles 25, the alloy additions,heating, cooling, gas supply and treatment times, so that the moltenaluminium reaches the casting stations 33, 34 in the desired quality, atthe desired temperature and fully homogenised.

By the use of ladles 25 according to the invention for the treatment andfeeding of molten aluminium in controllable sequences to preferablyseveral casting stations 33, 34, this process phase is decoupled interms of time from the actual casting process. The individual treatmentsare no longer predetermined and limited in terms of time, but can beadjusted as required, until the desired quality of the molten aluminiumto be cast is achieved in the respective ladle. If, for example, a lowerhydrogen content is required, the gas purification period can beextended. This option did not exist in the traditional in-line processaccording to FIG. 1. The production output of the casting machinedepends on the actual casting process, solely at the casting stations,which can be continued until the supply of the treated molten aluminiumto the casting stations is interrupted as required.

The method according to the invention is considerably more efficientthan the in-line process, since there is no longer any need for largerefining furnaces. If used at all, the furnaces are used for smeltingand heating, but not for keeping the melt warm over longer periods.These can be in the form of energy-efficient and ecologicallyadvantageous induction furnaces. By pre-heating the ladles, the smeltingtemperature achievable in the furnaces can be lower.

1. Casting method for aluminium or aluminium alloys, in which moltenaluminium is treated and fed to at least one casting station (33, 34),in which the molten aluminium is cast into semi-finished products orsimilar, characterised in that a number of ladles (25) are used to treatand to feed the molten aluminium to the respective casting station (33,34), the melt being poured into said ladles, transported to a furtherstage (32) and treated there, and is then delivered to the castingstation (33, 34), in which the ladles (25) are emptied.
 2. Castingmethod according to claim 1, characterised in that in a further stage(30) the emptied ladles (25) are cleaned and prepared for re-use, inparticular are pre-heated.
 3. Casting method according to claim 1,characterised in that in the first stage (21) the melt is poured fromone or alternatively from several furnaces (22, 23, 24) into the ladles(25), whereby if there are several furnaces (22, 23, 24) moltenaluminium of varying quality from the individual furnaces (22, 23, 24)can be poured into the ladles (25).
 4. Casting method according to claim3, characterised in that induction furnaces are used in the first stage(21).
 5. Casting methods according to claim 1, characterised in thatafter filling the respective pan (25), the dross is skimmed off thesurface of the melting bath (dedrossing) to which end the pan is broughtinto a tilted position.
 6. Casting method according to claim 1,characterised in that the second stage (32) includes the addition ofalloying additions to the melt, their purification and homogenisationand also if necessary any temperature regulation.
 7. Casting methodaccording to claim 6, characterised in that in the second treatmentstage (32), the ladles (25) can be placed underneath an immersiblerotary impeller to blow in argon or nitrogen for combined removal ofhydrogen, homogenisation and if necessary, thermal regulation, wherebyadditional small amounts of chlorine can be mixed into the purge gas toremove alkali trace contaminants.
 8. Casting method according to claim2, characterised in that at least part of the alloy additions has beenplaced in the emptied and cleaned ladles (25) before the moltenaluminium is poured in.
 9. Casting methods according to claim 1,characterised in that the ladles (25) run through the individualstations or stages on rails or by means of overhead hoists, wherebymultiple routes lead to preferably several casting stations (33, 34),and to additional storage stations (S) to store ladles (25) filled withmolten aluminium and/or empty ones until use.
 10. Casting methodaccording to claim 1, characterised in that the emptying of the ladles(25) occurs at the respective casting station (33, 34) through the baseof the ladles by controlled opening of a sliding closure, whereby theoutflowing molten aluminium is guided into a collector spout preferablyencased by an inert gas.
 11. Casting method according to claim 6,characterised in that the filling of the ladles (25) with moltenaluminium, if necessary with mixed material from various furnaces (22,23, 24), the addition of the alloy additions, homogenisation, thermalregulation and chronological sequence of treatment and feeding of themolten aluminium to the selected casting station (33, 34), iscomputer-controlled.
 12. Casting method according to claim 1,characterised in that the respective casting station (33, 34) operatescontinuously or semi-continuously and is equipped with a filter system.13. Casting machine to carry out the process according to claim 1, withat least one casting station (33, 34) and with means of treating andfeeding molten aluminium to the casting station (33, 34), characterisedin that the means of treating and feeding molten aluminium comprise anumber of ladles (25) fillable in a first filling station (21) with themolten aluminium, which are transportable to a second treatment station(32) and from there to the respective casting station (33, 34), wherebymultiple routes for the transport are provided, and the ladles (25) areeach fitted with a sliding closure or similar, by the opening of whichthey can be emptied.
 14. Casting machine according to claim 13,characterised in that a further purification and preparation station(30) is provided for the emptied ladles (25), from which the ladles (25)are transportable to the filling station (21).
 15. Casting machineaccording to claim 13, characterised in that additional storage stations(S) are provided for storage of ladles (25) filled with molten aluminiumand/or emptied ladles (25) until use.
 16. Casting machine according toclaim 13, characterised in that the filling station (21) is providedwith a number of furnaces (22, 23, 24) which can be supplied with basicmaterial, preferably induction furnaces, whereby the individual furnaces(22, 23, 24) can if necessary be supplied with aluminium material ofvarying quality.
 17. Casting machine according to claim 13,characterised in that the ladles (25) can be covered by a cover in whicha burner can be installed to maintain or to increase the temperature ofthe molten aluminium.
 18. Casting machine according to claim 13,characterised in that the ladles (25) are equipped with a porous plugfor injection of an inert gas.
 19. Casting machine according to claim13, characterised in that rails or hoists are provided for the transportof the ladles (25) from one station to the next and to the storagestations (S).